Actuators employing piezoelectric ceramics are those using the inverse piezoelectric effect, that when an electric field is applied, mechanical strain and stress are generated. Such actuators possess characteristics, such as generating large stress as well as being capable of gaining very small displacement with high precision. And such actuators are used, for example, in the positioning of precision machine tools or optical devices. In most cases, lead zirconate titanate (PZT), which has excellent piezoelectric properties, is used as the piezoelectric ceramic in the actuators. However, since lead zirconate titanate (PZT) contains a large amount of lead (Pb), the development of lead(Pb)-free piezoelectric ceramics as a substitute for lead zirconate titanate (PZT) have therefore been demanded, and various types of lead-free piezoelectric ceramics have been proposed to meet this demand.
A piezoelectric ceramic made of lithium potassium sodium niobate has been proposed in Patent Documents 1 and 2. The piezoelectric ceramic has a high Curie temperature of 350° C. or more, and also has an excellent electromechanical coupling factor kr.
Also, a piezoelectric material which comprises a compound obtained by replacing a portion of niobium (Nb) in sodium potassium lithium niobate with tantalum (Ta), and a perovskite oxide containing zirconium, alkaline earth metal elements such as strontium (Sr) and the like, have been proposed in Patent Documents 3 and 4. This piezoelectric material is attracting attention because it exhibits a relatively large displacement.